The long-term goal of this research is to establish well defined in vitro models for the regulation of cholesterol synthesis and to elucidate the molecular and biochemical mechanisms controlling the level and activity of 3-hydroxy-3-methylglutaryl (HMG)-Coenzyme A reductase and cholesterol synthesis. The approach is to determine the site and mechanism through which cholesterol and oxygenated sterols regulate the level and activity of HMG-CoA reductase in established liver cell lines of rat and human origin. We shall isolate and characterize regulatory variants resistant to the competitive inhibitor of HMG-CoA reductase ML-236B. We shall employ an immunochemical approach to the determination of rates of synthesis and degradation of HMG-CoA reductase in normal and mutant cells exposed to cholesterol and various inhibitors of HMG-CoA reductase.